Run ipcs with no arguments to see all three types of IPC objects:

For each IPC object, ipcs shows:

• key — the IPC key (in hex)
• id (shmid/semid/msqid) — the integer identifier
• owner — username of the owner
• perms — permission mask in octal
• Object-specific info (size, nattch, nsems, messages, etc.)

ipcrm removes a specific IPC object. You can identify the object by either its key or its identifier:

/* create_ipc_objects.c — create objects that you can inspect with ipcs */
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <sys/sem.h>
#include <sys/shm.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(void) {
    int msqid, semid, shmid;

    /* Create one of each type */
    msqid = msgget(IPC_PRIVATE, 0600);
    semid = semget(IPC_PRIVATE, 3, 0600);  /* set of 3 semaphores */
    shmid = shmget(IPC_PRIVATE, 8192, 0600);

    if (msqid == -1 || semid == -1 || shmid == -1) {
        perror("get call failed");
        exit(EXIT_FAILURE);
    }

    printf("Created IPC objects (PID=%d):\n", getpid());
    printf("  Message Queue ID: %d\n", msqid);
    printf("  Semaphore Set ID: %d\n", semid);
    printf("  Shared Memory ID: %d\n", shmid);
    printf("\nRun 'ipcs' in another terminal to see these objects.\n");
    printf("Run 'ipcrm -q %d' to delete the queue.\n", msqid);
    printf("Run 'ipcrm -s %d' to delete the semaphore set.\n", semid);
    printf("Run 'ipcrm -m %d' to delete the shared memory.\n", shmid);
    printf("\nPress Enter to delete and exit...\n");
    getchar();

    /* Cleanup */
    msgctl(msqid, IPC_RMID, NULL);
    semctl(semid, 0, IPC_RMID);
    shmctl(shmid, IPC_RMID, NULL);
    printf("All IPC objects deleted.\n");

    return 0;
}

You can programmatically list IPC objects by reading the /proc/sysvipc files (covered in detail in the next tutorial). Here’s a preview:

/* list_ipc_proc.c — list IPC objects by reading /proc/sysvipc */
#include <stdio.h>
#include <stdlib.h>

void list_ipc_type(const char *proc_file, const char *type_name) {
    FILE *f = fopen(proc_file, "r");
    if (!f) {
        perror(proc_file);
        return;
    }

    printf("\n=== %s (%s) ===\n", type_name, proc_file);
    char line[512];
    int first = 1;
    while (fgets(line, sizeof(line), f)) {
        if (first) {
            /* Print header line */
            printf("Header: %s", line);
            first = 0;
        } else {
            printf("Entry:  %s", line);
        }
    }
    if (first) printf("(no objects)\n");
    fclose(f);
}

int main(void) {
    printf("Listing all System V IPC objects via /proc/sysvipc:\n");

    list_ipc_type("/proc/sysvipc/msg", "Message Queues");
    list_ipc_type("/proc/sysvipc/sem", "Semaphore Sets");
    list_ipc_type("/proc/sysvipc/shm", "Shared Memory Segments");

    return 0;
}

#!/bin/bash
# cleanup_ipc.sh — Remove all System V IPC objects owned by current user

USER=$(whoami)
echo "Cleaning up IPC objects owned by: $USER"

# Remove message queues owned by this user
ipcs -q | awk -v user="$USER" '$3 == user {print $2}' | while read id; do
    echo "  Deleting message queue ID=$id"
    ipcrm -q "$id"
done

# Remove semaphore sets owned by this user
ipcs -s | awk -v user="$USER" '$3 == user {print $2}' | while read id; do
    echo "  Deleting semaphore set ID=$id"
    ipcrm -s "$id"
done

# Remove shared memory segments owned by this user
ipcs -m | awk -v user="$USER" '$3 == user {print $2}' | while read id; do
    echo "  Deleting shared memory segment ID=$id"
    ipcrm -m "$id"
done

echo "Done. Remaining IPC objects:"
ipcs